Gear pump



L. J. SINGELS May 12, 1970 GEAR PUMP Filed May 22, 1968 INVENTOR United States Patent 3,511,581 GEAR PUMP Louis Johan Singels, The Hague, Netherlands, assignor to Fuelmaster Produktie Maatschappij N.V. t/a Fuelinaater Manufacturing Company, The Hague, Netheran s Filed May 22, 1968, Ser. No. 749,523 Claims priority, application Netherlands, June 1, 1967 6707668 Int. Cl. F04c 17/06 US. Cl. 417-310 7 Claims ABSTRACT OF THE DISCLOSURE This application describes an internal gear pump for use as a fuel pump for oil burners. The pump is provided in its housing with a small channel through which air or gas, contained in the liquid to be pumped, may be fed back from the tooth spaces to the inlet side of the pump, so as to reduce or eliminate the noise caused by the presence of a gaseous medium in the liquid pumped.

The invention relates to gear pumps such as are used as fuel pumps for combustion apparatus operating on liquid fuel. Of such pumps a plurality of types are known. A first distinction is that between pumps with external gearing and those with internal gearing. Another distinction is that between those pumps in which the liquid present within a tooth space of a wheel can readily escape from this space upon penetration of a tooth of the other wheel, and those pumps in which the liquid trapped within a tooth space, when this space is reduced by penetration of the other wheels tooth, gradually increases in pressure before the liquid can escape from the space. The invention is particularly concerned with pumps of the last mentioned type, usually constructed as internal gear pumps and has for its object to remove a disadvantage inherent in these pumps.

This difficulty is caused by the fact that in practically all cases gas or air bubbles are present in the liquid to be pumped or are formed in the liquid during its transport. This can be due to various causes. It is, for example, exceedingly diificult to render the suction line of the pump absolutely airtight; with even a very small degree of untightness air enters into this line and is taken along with the liquid. Further, air or a gas may be dissolved in the liquid and, upon decrease of pressure caused by the suction of the pump, get free in the form of small bubbles,

whereas also such a decrease of pressure may sometimes bring about a partial evaporation of the liquid.

This air or gas will enter the suction side of the pump as a bubble, often formed by the joining of a number of smaller bubbles, and be transported by the gear wheels to the pumps exit, while being compressed by the increase in pressure.

Such air or gas bubbles can be a real hindrance in fuel pumps for oil burners, as they give rise to a very loud and annoying noise in the pump and the apparatus connected therewith (automatic valves and the like). The hindering noise increases as the pump has to produce a greater suction, in such a way that the limit put to the acceptability of the noise simultaneously puts a limit to the suction force, in other words to the vacuum which can be reached.

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The invention aims at removing the difiiculty mentioned bypreventing the air or gas from producing the hindering no1se.

To that end a gear pump according to the invention, in which the liquid in the tooth spaces is gradually increased in pressure, is provided in the housing enclosing the gear wheels with a channel of small passage area, which, with working pump, successively, puts each tooth space in communication with the suction side of the pump at such a place that in the tooth space a pressure prevails, which is superior to the pressure at the suction side of the pump but inferior to the pressure at the pressure side of the pump.

It was found that by this measure the hindering noise is fully or at least largely eliminated, as a result of which a higher vacuum can be produced by the pump without any objection. The explanation of this favourable result may be found in that, when a tooth space, filled for a greater part with gas or air of already increased pressure, gets into communication with the channel mentioned, the gas or air will escape through the channel to the suction side of the pump, so that bubbles of larger volume will no more reach the outlet port of the pump. Smaller bubbles may, it is true, remain behind in the tooth space and be carried on to the pumps exit and the discharge line, but it has been proved that small bubbles below a certain dimension will not produce the hindering noise. The quantity of air or gas discharged from a tooth space through the narrow channel again arrives at the suction side of the pump, but is split up into small bubbles when passing through the narrow channel and expanding into the liquid under lower pressure at the suction side of the pump. These small bubbles are again sucked in by the pump together with liquid and, partly, carried to the pumps discharge port, but owing to their small dimensions do not produce the unfavourable effect large bubbles have.

The result of the measure according to the invention can thus be shortly described as an elimination of large bubbles. It goes without saying that through the narrow channel liquid also will be able to escape from a tooth space towards the pumps suction side. However, through its higher viscosity as compared with gas or air, this quantity of liquid is very much limited and it affects the pumps capacity only in a negligible degree.

The channel described would however be able to annul the self-starting action of the empty pump, because through this channel air under pressure would be continuously led to the suction side of the pump. In order to maintain the self-starting action a loaded valve can be arranged where the said channel is connected to the suction side of the pump, said valve opening, only under a given pressure difference towards the suction side. When, at starting of the pump, the latter sucks in and pumps only air, the pressure difference between a tooth space filled with compressed air and the still small vacuum in the suction line is not suflicient to open the valve, the channel thus remaining inactive.

The invention will be described in more detail with reference to the drawing.

The drawing shows diagrammatically only those parts of a pump constructed according to the invention which are of importance for the understanding of the invention.

FIG. 1 is, on a larger scale, a section over the line II in FIG. 2; and

FIG. 2 is a view on the gear wheels, taken according to the line IIII in FIG. 1.

The pump shown in the drawing is an internal gear pump, providing spaces between the teeth of the annular gear wheel 1 and those of the gear Wheel 2. The number of teeth of gear wheel 2 is one lower than that of gear wheel 1, and the shape of the teeth is selected in such a way that the succeeding spaces do not, practically speaking, inter-communicate, the teeth of the inner and the outer gear wheel approaching each other between two spaces with substantially no play. The wheels are enclosed within a space formed by the pumps housing 5, the ring 4 and the cover plate 6, the ring 4 and the cover plate being fastened to the housing 5 by means of screws or bolts (not shown in the drawing) or by any other suitable means. The gear wheel 2 is driven by a shaft 3 and when rotating, drives the annular gear wheel 1.

Upon rotation in the direction indicated in FIG. 2 by an arrow, the volume of the tooth spaces at the right hand side of the figure gradually increases, as the left hand side gradually decreases; thus a sucking action appears at the right hand side, a pressing action at the left hand side. The liquid is supplied to the tooth spaces, via a diagrammatically indicated boring 7 of the cover plate 6, from the suction chamber 9 enclosed by a cap 10. The liquid is discharged through the discharge port 8 arranged in the housing 5, as diagrammatically indicated in the drawing. The suction chamber 9 is equipped with a filter 11 and connected to the suction line of the pump.

According to the invention a groove 12 is provided in the cover plate 6. The depth of the groove, for clearness sake exaggerated in the drawing, as well as its width amounts to only some hundredths of a millimeter, e.g. about 0.05 mm. (23 The groove is, as can be seen in FIG. 2 arranged in such a way that the same comes into communication with the passing tooth spaces, when these spaces are subjected to a reduction in volume, i.e. when in these spaces (with the pump operating) already a certain liquid pressure has been built up, which pressure however is still substantially below the final discharge pressure. The groove 12 debouches via a small chamber 13 into the suction chamber 9. Within the chamber 13 a spring loaded valve (14, 15) is arranged. An O-ring may serve as a seat for the valve.

The operation of the pump is as follows:

If the liquid does not contain any air or gas bubbles, the pressure difference between a tooth space, coming into communication with the groove 12, and the suction chamber will cause a flow of liquid to the suction chamber which, due to the narrowness of the groove and the viscosity of the liquid, will however be very small. The spring load on the valve 15 should be of course such that this valve opens. If the liquid sucked by the pump contains only small gas or air bubbles, distributed over the liquid, the picture is not substantially changed; these small bubbles are carried by the pump towards the pump outlet together with the liquid and do not give rise, as mentioned above, to a hinderance of any importance. If however a larger bubble reaches a tooth space through the inlet port 7, so that this space is occupied for a large part by the gaseous medium, then, when the space reaches the groove 12, the pressurized gaseous medium will escape through the groove 12 and the valve 15 towards the suction chamber 9, where the bubble explodes to a plurality of smaller bubbles through its rather sudden expansion. These smaller bubbles will, it is true, reach again the inlet port of the pump, but do not then cause any appreciable nuisance. On the contrary they bring about a decrease of the noise which as a rule accompanies the transport of oil through the gears. It is to be noted that, due to the considerable lower viscosity of the gaseous medium as compared with the liquid, the volume of the gaseous medium which escapes will be a multiple of the liquid which leaks away.

For the operation as described above the presence of the small valve 15 is not of any necessity. This valve serves for maintaining the selfstarting action of the pump. When at starting of the pump the inlet line and the pump itself are filled with air, the groove 12 would lead back to the suction side of the pump such an amount of air that a sufficient vacuum could not be established in the suction line. Now the valve 15 prevents such a return of air because the pressure load on the valve suifices to keep it closed. For the pressure rise occurring at the place of the groove when air is being pumped is substantially lower than when liquid or liquid with gas or air is being pumped, whereas on the other hand the Vacuum at the inlet side has not yet reached its maximum value.

The invention can be applied to other gear pumps than that shown in the drawing, e.g. to such pumps in which the difference between the pitch circles of the internally and externally toothed gear wheels is so large that a separate element, e;g. crescent shaped element is to be provided for separating the tooth spaces with suction action from those with pressure action. The construction of the channel for the escape of the gaseous medium as an open groove is most suitable from the standpoint of manufacturing, but other constructions are possible, e.g. the passage may be formed as a narrow boring passing through the cover plate 6.

Although the pump according to the invention is particularly suited as an oil pump for oil burners it may be used for other purposes in cases where difiiculties as described are met with.

I claim:

1. Internal gear pump comprising an internally toothed annular gear wheel and an externally toothed gear wheel, the teeth of the wheels defining tooth spaces which upon rotation of the wheels successively increase and decrease in volume, the teeth of the two Wheels touching each other in a substantially liquid tight manner; an enclosure for said wheels with a liquid inlet port in the area where the tooth spaces increase in volume and a liquid outlet port in the area where the tooth spaces decrease in volume; a liquid inlet chamber connected to the said inlet port; and a passage of exceedingly relatively small area in cross section as compared to the area of either the inlet or outlet ports leading from the enclosure at a place where the tooth spaces decrease in volume but in the direction of rotation before the place of the outlet port, to the liquid inlet chamber.

2. Internal gear pump according to claim 1, in which the passage of small area is constituted by a groove in a side wall of the enclosure.

3. Internal gear pump according to claim 1, in which the passage of small area is constituted by a groove in a side wall of the enclosure, said groove having a depth and width less than $1 4. Internal gear pump according to claim 1, in which the passage of small area debouches into the liquid inlet chamber via a small loaded valve, opening towards the said chamber.

5. Internal gear pump comprising an internally toothed annular gear wheel and an externally toothed gear wheel, the second wheel having one tooth less than the first wheel and the teeth of the two wheels touching each other in a substantially liquidtight manner, so as to define tooth spaces which upon rotation of the wheels successively increase and decrease in volume; an enclosure for said wheels comprising side Walls, one of said side walls having an inlet port in the area where the tooth spaces increase in volume and the other Wall having an outlet port in the area where the tooth spaces decrease in volume; a liquid inlet chamber connected to the said inlet port; and a groove of relatively small depth and width as compared with the area of either the inlet or the outlet ports provided in the wall with the inlet port, leading from the enclosure at a place where the tooth spaces decrease in volume but have not yet reached the outlet port, to the liquid inlet chamber.

6. Internal gear pump according to claim 5 in which the said groove has a depth and width less than 1 7. Internal gear pump according to claim 4 in which References Cited UNITED STATES PATENTS 2,471,149 5/ 1949 Girz. 2,513,984 7/ 1950 Witchger. 2,732,802 1/1956 Eames.

6 3,137,234 6/ 1964 Mosbacher. 3,267,862 8/ 1966 Mosbacher. 3,272,128 9/1966 Brundage.

WILLIAM L. FREEH, Primary Examiner W. I. GOODIN, Assistant Examiner US. Cl. X.R. 418-79 

